Lesson 9: Question 5

[T.B.Justin]

I have a question concerning the wording of the correct answer choice (A):

"The failure of cited evidence to establish a statement is taken as evidence that that statement is false."

Where is the failure in the cited evidence of establishing a statement? I think that "two of the stones that determine a line pointing directly to the position of the sun at sunrise at the spring equinox" is the cited evidence, and that it does in fact establish the statement of some historians that claim, "the people that built 'that' ring of stones thousands of years ago in Britain were knowledgable about celestial events."

I think Dobson takes that established statement and asserts it is false.

Also, is this a lack of evidence for a position is taken to prove that position is false?

[Jay Donnell]

Hey T.B.!

This is a representation of a common but tricky logical fallacy, and one that requires two viewpoints to occur.

Let's open up with an example:

I am your defense attorney, and you, my client, have been accused of murder.

I'm feeling great about our case, as you've told me you didn't leave your house that night and the murder was committed all the way across town.

So there we are in court, and I use your being nowhere near the crime scene as the evidence for my claim that you are innocent.

However, a witness is called to the stand who produces a selfie that they took with you while out at the movie theater during the night in question.

I'm starting to panic, because that evidence just completely ruins the case I was building for your innocence. The evidence I was using toward my conclusion is no longer viable, but does that make my conclusion false?

Though I no longer have any evidence that you are innocent, there remains (from what I've discussed so far) no evidence for your guilt, either.

So, if the jury found you guilty on the basis of what happened with this witness, they would have committed the same fallacy as the one committed in the stimulus in question.

Turns out the evidence of your testimony that you didn't leave your house that night does not establish my claim of your innocence, but that failure doesn't work as evidence to prove my claim as false.


In this question, the evidence given by 'some historians' to support their claim that "The people who built a ring of stones thousands of years ago in Britain were knowledgeable about celestial events" involves how some of the stone placements match up to the sun's position at sunrise during the Spring equinox.

The author of the passage then dismisses the relevance of that evidence by implying that with so many stones scattered around, the odds were high that they would match up with some celestial pattern merely by random chance.

That idea should have been used to damage the original claim made by the historians, which now loses much luster as their claim depended heavily on the implications of that rock placement in relation to the sun's positioning. However, the author (Dobson) overshot his/her range when they concluded that "the people who built the ring were not knowledgeable about celestial events," which is essentially saying that the historians claim is false.

This does fit neatly into one of the evidence fallacies discussed in the course books, exactly as you had identified!

This can certainly be understood under the broader umbrella of: A lack of evidence for a position is taken to prove that position is false

Maybe these people did have knowledge about celestial events? This evidence not panning out shouldn't rule out other existing evidence that could help prove the conclusion here, much the same as it could with your innocence in our mock trial example above.

Now let's both go watch This Is Spinal Tap and laugh as they rock around their tiny Stonehenge mode on stage